There is known a technology for improving combustion efficiency, etc. of an internal combustion engine through use of a variable valve actuation system, which variably controls a valve timing, an event angle, and a lift amount of intake and exhaust valves in accordance with a running condition.
For example, JP 2008-95668A discloses a variable valve actuation system capable of variably controlling, in a so-called dual-intake valve internal combustion engine including two intake valves for each cylinder, a valve timing and the like of one intake valve while maintaining a fixed valve timing and the like of the other intake valve. More specifically, an opening timing of the intake valve on the fixed side is set to a top dead center and a closing timing thereof is set to a bottom dead center, whereas an opening timing of the intake valve on the variable side is fixed to the top dead center and a closing timing thereof is variably controlled. In other words, the opening timings of both the intake valves are fixed to the top dead center, and only the closing timing of the intake valve on the variable side is changed.